text: /**
   * PANDA 3D SOFTWARE
   * Copyright (c) Carnegie Mellon University.  All rights reserved.
   *
   * All use of this software is subject to the terms of the revised BSD
   * license.  You should have received a copy of this license along
   * with this source code in a file named "LICENSE."
   *
   * @file primeNumberGenerator.cxx
   * @author drose
   * @date 2001-03-22
   */
  
  #include "primeNumberGenerator.h"
  
  
  /**
   *
   */
  PrimeNumberGenerator::
  PrimeNumberGenerator() {
    _primes.push_back(2);
  }
  
  /**
   * Returns the nth prime number.  this[0] returns 2, this[1] returns 3;
   * successively larger values of n return larger prime numbers, up to the
   * largest prime number that can be represented in an int.
   */
  int PrimeNumberGenerator::
  operator [] (int n) {
    nassertr(n >= 0, 0);
  
    // Compute the prime numbers between the last-computed prime number and n.
    int candidate = _primes.back() + 1;
    while ((int)_primes.size() <= n) {
      // Is candidate prime?  It is not if any one of the already-found prime
      // numbers (up to its square root) divides it evenly.
      bool maybe_prime = true;
      int j = 0;
      while (maybe_prime && _primes[j] * _primes[j] <= candidate) {
        if ((_primes[j] * (candidate / _primes[j])) == candidate) {
          // This one is not prime.
          maybe_prime = false;
        }
        j++;
        nassertr(j < (int)_primes.size(), 0);
      }
      if (maybe_prime) {
        // Hey, we found a prime!
        _primes.push_back(candidate);
      }
      candidate++;
    }
  
    return _primes[n];
  }
  